Olivier Fourdan authored Jun 05, 2018 and Adam Jackson committed Jun 21, 2018

To be able to check for availability of the Wayland interfaces required
to run a given EGL backend (either GBM or EGLStream for now), we need
to have each backend structures and vfuncs in place before we enter the
Wayland registry dance.

That basically means that we should init all backends at first, connect
to the Wayland compositor and query the available interfaces and then
decide which backend is available and should be used (or none if either
the Wayland interfaces or the EGL extensions are not available).

For this purpose, hold an egl_backend struct for each backend we are to
consider prior to connect to the Wayland display so that, when we get to
query the Wayland interfaces, everything is in place for each backend to
handle the various Wayland interfaces.

Eventually, when we need to chose which EGL backend to use for glamor,
the available Wayland interfaces and EGL extensions available are all
known to Xwayland.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>